Americans buying their favorite fruit may see signs at the produce stand announcing that the bunches are "Eco-OK."

That means the companies that grow the fruit are meeting environmental and social standards set by green groups. And bananas are just the latest Latin American crop. Heightened social responsibility is spreading from the banana plantations to coffee, cacao, sugar, and citrus producers. The food industry has caught on that, in this time of prosperity, Americans are willing to pay more to feel good about what they eat.

"It's smart business as well as environmentally and socially sound," says Bill Liebhardt, of the Sustainable Agriculture Research and Education Program at the University of California at Davis. "It builds a better position in the marketplace. It's part of good business to present your product as environmentally benign or beneficial and to say that you pay your workers a good salary."

Last month, a sign of change in the banana business came when Ecuador's second largest producer, Reybancorp, earned the right to use the Eco-OK seal of the Better Banana Project. By early fall, Chiquita, one of the top three banana producers (along with Dole and Del Monte), will qualify as well.

"When you take those two companies together, it means a transformation of the banana industry," says Chris Wille, who works for the Rainforest Alliance out of Costa Rica. As of this spring, about 30 percent of banana production in Costa Rica and 70 percent in Panama had been certified. Mr. Wille puts production of Better-Banana-Project-certified farms at 60 million boxes, or 10 percent of Latin American and Caribbean production.

Banana growers' legacy of abuses to both land and humans at one point led to talk of boycotts. But in a nation like Costa Rica, where 50,000 families depend on the sweet yellow fruit, a boycott would have harmed more than helped.

"Instead of throwing people out of work," says Wille, "we looked at giving guidance to the industry and rewarding the good actors by giving them an eco-label that they can use to distinguish themselves in the marketplace."

One example of the changes taking place: When Wille first arrived in Costa Rica 10 years ago, he saw rivers choked with blue plastic bags, used by growers to control ripening and protect the fruit from insects.

The bags used to be stripped off and thrown into piles that were carried off in floodwater. Now, on all certified farms, they are collected and recycled.

Even people within the industry admit the business needed to do something.

"The banana industry has a reputation of misuse of chemicals and poor treatment of workers," says Rafael Wong, president of Reybancorp. Now, the firm will meet standards set by the Conservation Agriculture Network, a coalition of Latin American environmental groups.

The program addresses a spectrum of socio-environmental issues. On certified farms, reforestation programs have replaced rampant deforestation. Workers receive improved housing, schools, training, and medical care - not to mention contracts and the right to organize. In addition, most certified farms pay workers above minimum wage. At Chiquita's Costa Rican farms, for example, workers make $12.90 a day - 176 percent more than the $7.33 minimum wage.

To maintain certification, farms must show continual improvements. Inspectors make surprise visits to farms and audit them annually.

Chiquita was the first multinational company to join the Better Banana Project, which began in 1991. "We will have all of our farms completed by the end of the summer or early fall," says Magnes Welsh, a Chiquita spokesman. The company's farms in Costa Rica, Panama, and Colombia are already fully certified.

"When a company as big as Chiquita is involved in this, it really has a ripple effect," says Wille.

Dole, too, is taking on a more verdant hue. Last month, it ranked among the Top 10 companies overall in environmental and social responsibility as ranked by the Council on Economic Priorities, a public-interest research organization.

"Large farms, in general, are hopping on board," says Dr. Liebhardt. "A lot of industries are trying to present themselves in as green a light as possible."

Many coffee farmers in Costa Rica have stopped dumping organic wastes from coffee mills into rivers, which was a major source of pollution. Also, under pressure from conservationists, some coffee farmers are returning to a traditional method of growing coffee in the shade of rain forest trees, which provides habitat for monkeys and birds. In Brazil, the sugar industry is phasing out the practice of burning fields before harvest.

The reason for all this is simple: money. American shoppers are more willing than ever to pay a premium for ecofriendly products.

For example, at Magic Mill, a natural-foods market in Madison, Wis., organic bananas - 99 cents a pound, compared with 39 cents for their ordinary brethren - are the second-highest seller, behind cherries.

It was the surging popularity of organic and ecofriendly products in the marketplace that, in part, motivated Ecuador's Reybancorp to put six years of effort into transforming their haciendas into ecohip farms. They replaced 65 to 75 percent of their infrastructure, planted hundreds of thousands of trees, and restored about 5,000 acres.

And it expects a return on its eco-investment. "We thought we would get a premium price if we did this," says Wong.